Ski construction and method of forming the same

ABSTRACT

A multi-layer ski that changes stiffness automatically responsive to snow temperature. The ski has an inner layer, a bottom layer and an outer layer on the top and side surfaces. The outer layer is formed from an elastomer, preferably a polyurethane having a thermal expansion coefficient between about 200 and 300 in/in/*Cx10 6.

United States Patent [1 1 Zemlin et al.

[ Sept. 11, 1973 1 SKI CONSTRUCTION AND METHOD OF FORMING THE SAME Inventors: John C. Zemlin, Reading; Glenn W.

Dow, Newburyport, both of Mass.

[73] Assignee: Graves Corporation, Newburyport,

Mass.

Filed: May 21, 1971 Appl. No.: 145,619

US. Cl 280/11.13 L Int. Cl. A63 5/12 Field of Search 2 80/11.13 L, 11.13 F,

References Cited UNITED STATES PATENTS 3,398,968 Mutzhas .1. 280/11.13 F

3,503,621 3/1970 Schmidt et al. 280/1 1.13 L 2,695,178 11/1954 Rheinfrank, .I'r. 280/1 1.13 L 3,393,918 7/1968 Styka 280/1 1.13 L

FOREIGN PATENTS OR APPLICATIONS 1,173,199 12/1969 Great Britain 280/l1.13 L

Primary Examiner-Leo Friaglia Assistant ExaminerMilton L. Smith Att0meyKenway, Jenney & l-lildreth [57] ABSTRACT A multi-layer ski that changes stiffness automatically 8 Claims, 4 Drawing Figures PATENTED SEP1 1 I975 INVEN'I'ORS JOHN C. ZEMLIN GLENN W. DOW

I TT NEYS w \K x \X t vm vm om v m 9% a H m N m 1 SKI CONSTRUCTION AND METHOD or FORMING THE SAME This invention relates to a multi-layer ski construction and to a method for forming the same. I

In skiing it is desirable to use a relatively stiff ski at low skiing temperatures and a relatively flexible ski at increased snow temperatures to obtain a uniform control of the ski under varying temperature conditions. Prior to the present invention, a wide variety of mechanical means have been provided for varying the ski flexibility by varying thetension on the ski. Generally, these means comprise a cable or.strip running the length of the ski and attached to both ends thereof either on the outside or through the interior of the ski and mechanical means for varying the tension on the cable or strip. Unfortunately, these proposals have severe drawbacks which has effectively prevented their use. First, the means for varying tension on the cable or strip generally become frozen and difficult to manuver under normal skiing conditions. Secondly, since variations in temperature generally occur throughout the ski run, mechanical means would have to be constantly adjusted to attain optimum performance. A non-mechanical means for controlling the tension of the ski is disclosed in U.S. Pat. No. 3,398,968 wherein a ski construction is shown comprising a running layer, a U-shaped outer housing attached to the running layer and two interior layers between the outer housing and the running layer each having a different thermal expansion coefficient so that when the ski temperature is changed, the difference in thermal expansion between the two layers results in a tension change along the entire length of the ski by causing the ski to be bent along its entire length. This structure for changing the elasticity of the ski is disadvantageous since it changes the built-in camber of the ski so that during use, the load will not be equalized over the length of the ski. When the load is not equalized over the length of the ski, turning becomes extremely difficult because of the unequal forces exerted on the snow at the ends of the ski as comapred with the middle of the ski depending upon how the camber is changed by the differential thermal expansion of the inner layers. Accordingly, it would be highly desirable to provide an automatic means for changing the flexibility of the ski responsive to changes is snow temperature without changing the built-in camber of the ski.

The present invention provides a multi-layer ski construction comprising an inner layer formed from a flexiblematerial such as fiber glass and/or wood which may or may not be modified with a density modifying agent such asfoam, and an outer layer on the two sides and the top of the ski comprising a thermoplastic material havinga thermal expansion coefficient, when cured, between about 200 and about 300 in/in/C l0. The bottom surface comprises a low friction material having metal edges running the length of the ski. In addi tion, the present invention provides a method for mold- 7 ing the skis of this invention whereby the outer layer is injected as a thixotropic moving plug into a mold containing an unfinished ski and then cured.

THe invention will be more fully described with reference to the accompanying drawings.

FIG. 3 is a vertical cross-sectional view of a ski in a mold used for applying the outer layer to the ski.

FIG. 4 is a cross-sectional view taken along line 44 of FIG. 3.

Referring to FIG. 1, the ski, generally indicated at l, is cambered at its midsection a distance from the horizontal sufficient to compensate for the weight placed on it during use so that the weight is distributed equally along the length of the ski. At the midsection of the ski along it length as shown, the ski 1 comprises three layers; namely, anouter layer 2 formed from a thermoplastic material having a thermal expansion coefficient between about 200 and 300 in/in/CX10", an inner layer 3, usually formed from fiber glass and/or wood and having a density reducing material 4 such as foam and a bottom layer 5 formed from a low friction material such as high density polyethylene. TH ski 1 also is provided with metal edges 6 and 7 to protect the ski at both ends.

FIG. 1 is a side view of a ski having a built-in camber.

FIG. 2 is a vertical cross-sectional view of the ski of FIG. 1 taken along line 2--2.

As shown in FIG. 2, the ski 1 also is provided with metal edges 8 and 9 which extend along its entire length. It is preferred that the outer layer 2 be slightly thicker at the intersection at the top and side surfaces along the length of the ski l to form bumpers 11 and 12 to provide added protection to the inner layer 3. In addition, since the bumpers 11 and 12 are formed from a relatively resilient material, they absorb the shock caused by sharp blows such as when the two skis contact during use. Thus, any sharp blows to the ski on these edges is not transferred along the length of the ski thereby resulting in a smoother ride.

The method for forming the outer layer is described with reference to FIGS. 3 and 4. The outer layer 2'is applied to the inner layer 3 by placing a partially made ski '15, in a mold comprising two mold sections 17 and 18 having an inlet 19 and an outlet 20. The ski 15 is positioned in the mold conveniently by magnetic means in the mold section 17 and 18 which align the metal edges 6, 7, 8 and 9. The top surface 21 comprising the inner layer is spaced apart from the inner surface 22 of the mold 18 by means of spacers 24 which are adhered to the partially finished ski 15. Uncured thennoplastic material which is subsequently cured to form the outer .layer, is introduced into the mold through inlet 19 as a highly viscous thixotropic material which passes along the length of the mold in the space between the partially finished ski l5 and the inner surface of the mold as a relatively stable plug. As the plug moves along the length of the mold, it pushes air out of outlet 20. The uncured material should be injected at a pressure above about 20 psig to ensure that it moves as a plug in the mold space. By operating in this manner, no air is entrapped between the unfinished ski and the outer layer or within the outer layer. After the material forming the outer layer has filled the mold, the mold is heated in any manner desired until the complete curing is effected. If desired, the surface 21 of the partially finished ski can be roughened or a layer added theretoto form a rough layer thereby promoting adhesion between the outer layer 2 in the inner layer Suitable elastomeric materials that can be employed as an outer layer have a glass transition point less than the materials employed in the remaining portion of the ski, are thixotropic in the uncured state and, when cured, have a thermal expansion coefficient between about 200 and 300 in/in/CXl0. Suitable materials include polyurethanes, silicones, EPDM rubbers, or

plasticized polyvinylchloride which may contain the usually employed additives including fillers, pigments and extenders. It is preferred to employ as an outer layer, a polyurethane formed by mixing a polyol and a diisocyanate to form a moderately reactive thixotropic mixture having a voscosity above about 1000 cps so that, when injected into the mold, it moves as a plug in the space between the ski and the mold surface. The polyol and diisocyanate are directed from separate storage containers to a mixing zone and the mixture is injected immediately into the mold. The polyol component contains the catalyst which promotes the polyurethane forming reaction and a filler in a concentration to regulate 'thixotropicity of the polyol-diisocyanate mixture.

it is preferred that the surface of the unfinished ski be roughened prior to applying the outer layer. The ski can be roughened either mechanically or by applying a rough thin coating. It is preferred to employ the latter method by brush-coating an epoxy layer on the unfinished ski surface;

Suitable polyols are the polyether polyols and polyester polyols which have an average molecular weight between about 300 and 4000, preferably between 500 and 2000 including polybutylene ether glycol, polyethylene ether glycol, polypropylene ether glycol, polyethylene adipate, polybutylene adipate, polyethylene sebacate, polycaprolactone or polyurethane prepolymers obtained by incompletely reacting a polyol with a diisocyanate, and mixtures thereof. Particularly suitable polyols are poly l, 4 butylene glycol, polyethylene adipate and polycaprolactones.

It is usually advantageous to incorporate a chain extender such as a lower molecular weight diol or triol such as l, 4 butane diol trimethylol propane ethylene glycol with the higher molecular weight polyol. In addition to or in place of the lower molecular weight diol or triol, low molecular weight amines are also useful such as hydrazine, MOCA, p-phenylene diamine and the like.

A variety of polyisocyanates may be reacted with these polyols to obtain satisfactory polyurethane compositions, particularly the aromatic diisocyanates as they are more reactive and less toxic than the aliphatic diisocyanates. Such diisocyanates include 2, 4-tolylene diisocyanate, 2,6-tolylene diisocyanate, naphthylene l, 4-diisocyanate, and diphenylmethane-4,4' diisocyanate, 3,3 '-dimethoxy biphenylene diisocyanate, 4, 4-diphenylene diisocyanate and mixtures thereof. The diisocyanate usually is employed in stoichiometric excess to assure complete reaction with the functional groups of the polyol and chain extender.

The following example illustrates this invention and is not intended to limit the same.

EXAMPLE I The multi-layer skiof this invention can be formed as follows.

A partially finished ski having metal tips and edges and formed by molding fiber glass strands extending the length of the final ski with a polyester alkyd resin and having a rigid polyurethane foam filler therein and a running surface comprising a high density, low friction polyethylene is placed into a mold shaped to the final ski desired. The metal edges of the unfinished ski are magnetically positioned in the mold to prevent contact of the side walls of the unfinished ski with the mold. Circular spacers are adhered to the top surface of the unfinished ski and the ski then is placed face down in the mold so that the top and side surfaces do not contact a mold surface. An uncured polyurethane mixture formed by admixing 1 part by weight of a polyethylene adipate polyol, 9 parts by weight of ethylene glycol and containing 3 parts by weight of a silica filler and 1.5 parts by weight of a pigment with 25 parts of a diisocyanate reactant comprising a polyethylene adipate based diisocyanate prepolymer. The resultant mixture is thixotropic and is injected into the mold in the space between the top surface of the unfinished ski and the mold surface so that air in the mold in that space is pushed out of the mold. The injection is continued until the polyurethane extends the length of the ski. After being injected, the polyurethane and ski are heated to a temperature between about F. and about F. for about 15 minutes. The mold then is open and the finished ski is removed therefrom.

We claim:

1. A multi-layer ski having a bottom layer, an inner layer and an outer layer, said outer layer comprising the top and side surfaces of the ski and comprising an elastomeric composition having a thermal expansion coefficient between about 200 and 300 in/in/C l0 so that during use, the outer layer changes the relative stiffness of the ski responsive to snow temperatures.

2. The ski of claim 1 wherein the outer layer comprises a cured polyurethane composition.

3. The ski of claim 1 wherein the inner layer comprises glass fibers extending the length of the ski and adhered with a polyester alkyd resin.

4. The ski of claim 2 wherein the inner layer 'comprises glass fibers extending the length of the ski and adhered with a polyester alkyd resin.

5. The ski of claim 1 wherein the outer layer is thicker at the intersections of the top and side surfaces than at the remaining portions of the outer layer.

6. The ski of claim 2 wherein the outer layer is thicker at the intersections of the top and side surfaces than at the remaining portions of the outer layer.

7. The ski of claim 3 wherein the outer layer is thicker at the intersections of the top and side surfaces than at the remaining portions of the outer layer.

8. The ski of claim 4 wherein the outer layer is thicker at the intersections of the top and side surfaces than at the remaining portions of the outer layer. 

2. The ski of claim 1 wherein the outer layer comprises a cured polyurethane composition.
 3. The ski of claim 1 wherein the inner layer comprises glass fibers extending the length of the ski and adhered with a polyester alkyd resin.
 4. The ski of claim 2 wherein the inner layer comprises glass fibers extending the length of the ski and adhered with a polyester alkyd resin.
 5. The ski of claim 1 wherein the outer layer is thicker at the intersections of the top and side surfaces than at the remaining portions of the outer layer.
 6. The ski of claim 2 wherein the outer layer is thicker at the intersections of the top and side surfaces than at the remaining portions of the outer layer.
 7. The ski of claim 3 wherein the outer layer is thicker at the intersections of the top and side surfaces than at the remaining portions of the outer layer.
 8. The ski of claim 4 wherein the outer layer is thicker at the intersections of the top and side surfaces than at the remaining portions of the outer layer. 